1. Field of the Invention
This invention relates to high-pressure pumps for electro-rheological fluids, and more particularly to pumps for such fluids which contain particulate matter in the range of 10 to 50 micron size.
2. Description of the Prior Art
As will be appreciated by those skilled in the art, electro-rheological fluids are slurries typically comprised of a non-conducting fluid and particulates. A typical slurry contains about 30% particulates and 6% water by eight mixed in a dielectric liquid. The application of a high-voltage electric field across a small gap filled with a electro-rheological fluid causes the water absorbed in the particulate to form induced dipoles which align the particles between the electrodes, resulting in an effective change in viscosity in the localized area between the electrodes. The particulates are normally on the order of 10 microns in diameter, and may be either hard or soft. Electro-rheological materials and some applications in which they are used are discussed in more detail in the literature, including the following articles, which are incorporated herein by reference.
Cyanamid, "Electro-Rheological Fluids", American Cyanamid Company, Wayne, New Jersey.
Machine Design, "Fluids That Thicken Electrically", by Theodore G. Duclos, Debra N. Acker and J. David Carlson, Thomas Lord Research Center, Lord Corporation, Cary, North Carolina; January 21,
Phys. Technology, Vol. 14 1983, The Institute of Physics, "Electrorheological Fluids" by J. E. Stangroom.
In general, pumps are used to build a high pressure in a hydraulic fluid. Positive displacement pumps such as gear pumps, IMO pumps, piston pumps, vane pumps, etc., are commonly used. These pumps all utilize close fitting components, typically steel components, to form cavities in which fluid is compressed to high pressures and discharged to a common manifold.
These pumps depend on close clearances of the components during operation using contaminant-free fluids. Systems in which such pumps are used are commonly filtered to remove particles larger than 10 microns because the pumps can be damaged by the ingestion of larger particles. Damage results typically from the contaminate scoring the surfaces of the close fitting components and causing excessive leakage.